Field of the Invention
The present invention relates to solid organic phosphites resistant to hydrolysis, and to the process for preparing them.
The organic phosphites are compounds which are used in the art in order to endow the organic polymers with stability characteristics, against the oxidative degradation caused by light and/or heat, such as disclosed, e.g., in U.K. Patent No. 803,557 and U.S. Pat. No. 3,516,963.
The organic phosphites suffer from the undesired characteristic of undergoing phenomena of hydrolysis, in particular during their storage under warm and moist conditions, with the consequent loss of stabilizing activity, and danger of handling problems arising.
It is known to coat solid phosphite powders with dialkoxy or diphenoxy substituted silicones such as those of the formula: ##STR1## wherein R.sup.5 is an alkoxy or phenoxy group and m is greater than 4. Such disubstituted silicones can however undergo a reaction with water, thereby generating an alcohol or phenol which can in turn react with the phosphite. Thus while coatings of disubstituted silicones can provide solid phosphites with some degree of protection from hydrolysis, they themselves can result in degradation through their secondary hydrolysis byproducts. Other processes for coating phosphites include treating said powder phosphites with a monomeric silane containing in its molecule at least two alkoxy groups and causing the silane to hydrolyze, thereby causing the formation of a siliconic polymer on the surface of powder particles but most likely liberating alcohol which promotes phosphite alcoholysis.
It is also known to blend organo amines with phosphites to improve the hydrolytic stability thereof, see York U.S. Pat. No. 4,116,926, issued Sep. 26, 1978, which discloses a phosphite composition comprising a small proportion of trisopropanolamine; and Hodan et al, U.S. Pat. No. 3,553,298, issued Jan. 5, 1971, which discloses phosphite ester compositions containing particular nitrogen-containing compounds which stabilize the phosphite ester against hydrolysis.
Consequently, there is a desire to improve the hydrolytic stability of silicone coated solid phosphites and silicone containing organic phosphite compositions.